Muscle weakness is a serious problem in the elderly which can be exacerbated by age-related diseases. A promising intervention is the pharmacological treatment with anabolic agents. such as beta- 2-adrenergic (B2AR) agonists. These drugs have been shown to increase muscle mass and specific force production (force per cross sectional area) in adult animals and humans. The general goal of this proposal is to improve our understanding of the effects of a B~-adrenergic agonist on senescent skeletal muscle. Specifically, this grant will address two questions: l) Will B2AR agonists increase locomotor and respiratory muscle power output in senescent rats?; and 2) Is the mechanism of the I32AR agonist- induced increase in muscle specific tension due to an increase in force production by each myosin cross bridge bound to actin? These questions will be addressed by using the tools of muscle physiology and biochemistry. Given that the loss of muscle mass with age can lead to many negative clinical consequences, it is important to develop strategies to maintain muscle mass and strength during aging. Therefore, the significance of this application is that these experiments will examine the anabolic effects of B2-agonists to determine their suitability for restoration of muscle mass and power generation in senescent animals. Further, the proposed experiments will determine the mechanism responsible for the B2-agonist-mediated increase in specific force production. An understanding of the basic mechanisms associated with this type of hypertrophy can provide the basis for the application of therapy as well as the development of new drugs for the treatment of many types of muscle wasting.